IL104019A - Mixtures of 1,1,1-trifluoroethane and perfluoropropane and their applications as refrigerants as aerosol propellants or as plastic foam-expanding agents - Google Patents

Abstract

To replace chlorofluorocarbons as refrigerating fluids, the invention proposes to employ mixtures containing, on a mass basis, approximately 40 to 70 % of 1,1,1-trifluoroethane and 30 to 60 % of perfluoropropane. The mixtures according to the invention can also be employed as aerosol propellants or as blowing agents for plastic foams.

Description

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Mixtures of Π ,1 ,1-trifluoroethane and perfluoropropane and their applications as refrigerants, as aerosol propel 1 ants or as plastic foam-expanding agents ELF ATOCHEM S.A.

C. 88246 The present invention relates to mixtures of refrigerants having a low boiling point which have little or no effect on the environment and are intended to replace chlorofluorocarbons (CFC) in pressurised low-temperature refrigeration systems.

It has now been established that, because of their significant action factor on ozone, the CFCs will, in the shorter or longer term, be replaced by refrigerants which no longer contain chlorine and, as a result, are less aggressive with respect to the environment. 1, 1, 1-trifluoroethane (HFC 143a) and perfluoropropane (FC 218) have, in comparison with the completely halogenated chlorinated compounds, a very small effect on the environment. HFC 143a has, however, the disadvantage of being inflammable. With regard to FC 218, its use in refrigeration is reflected in a relatively poor refrigerating capacity, a high compression ratio and, consequently, high operating costs .

It has now been found that mixtures containing, by weight, about 40 to 70 % of HFC 143a and 30 to 60 % of FC 218 have a maximum vapour pressure in comparison with the vapour pressures of the pure compounds .

On the other hand, for mass fractions of HFC 143a of between 41 and 60.3 % and of FC 218 of between 39.7 and 59 %, the mixtures show a pseudo-azeotropic behaviour and are non-inflammable, in contrast to HFC 143 a.

It has also been found that the two constituents together form an azeotrope which has a minimum boiling point of about -49.8eC under 1.013 bar and in which the HFC 143a content at the normal boiling point is about 55 % by mass and that of FC 218 about 45 %.

Because of their low boiling point, the mixtures according to the invention may be used as refrigerants in low-temperature (-40 °C; -50 eC) applications, as in the case of low-temperature industrial or commercial refrigeration. The azeotrope described above. is a refrigerant mixture- hich is. very particularly preferred.

In the light of their physical properties, which are close to those of the CFCs, the mixtures according to the invention may also be used as aerosol propellants or. as plastic foam-expanding, agents.

The following examples illustrate the invention, without restricting it.

EXAMPLE 1 The azeotrope according to the invention has been studied experimentally at various temperatures by gas phase chromatographic analysis of the compositions of the liquid phase and of the vapour phase for various mixtures of HFC 143a and FC 218.

The pressures were measured to an accuracy of greater than 0.02 bar using a HEISE manometer. The temperatures were measured to an accuracy of 0.02°C using a 1000 ohm platinum probe.

The appended graph 1 shows the liquid/vapour equilibrium curve of HFC 143a/FC 218 mixtures, recorded at a temperature of -0.4°C. In this graph, the abscissa axis indicates the mass fraction of HFC 143a and the ordinate axis the absolute pressure in bars; the black squares correspond to the experimental points.

A curve analogous to that of graph 1 is obtained for each temperature. By successive additions of HFC 143a to the FC 218, the pressure developed by the mixture increases regularly, then passes through a maximum and falls regularly, this demonstrating the existence of the azeotrope of minimum boiling point.

EXAMPLE 2 The HFC 143a/FC 218 azeotrope was also demonstrated experimentally by determining the boiling point under 1.013 bar for various mixtures of HFC 143a and FC 218.

The pressures were determined to a precision of greater than 0.005 bar using a HEISE manometer. The temperatures were adjusted in 0.1eC steps in order to obtain a pressure of 1.013 bar.

The normal boiling points determined in this way for various compositions containing HFC 143a and FC 218 are indicated in the following table: TABLE 1 The results in this table demonstrate a minimum normal boiling point for a mass fraction of HFC 143a of about 44.7-54.8 %. However, it is pointed out that the mixture behaves as a quasi-azeotrope for mass fractions of HFC 143a of 41 to 60.3 %.

The correlation of the experimental points thus obtained was carried out in accordance with well-known techniques, using computer simulation.

The results of these correlations demonstrate the minimum normal boiling point for a mass fraction of HFC 143a of 55 %; this enables the azeotrope to be characterised by: . its normal boiling point, which is about -49.8eC . its HFC 143a content, by mass, in the composition, which is about 55 %.

Table 2 below gives the pressure/temperature relationship for a mixture containing, by mass, about 55 % of HFC 143a and 45 % of FC 218, compared with that of the pure substances.

TABLE 2 The vapour pressure of the azeotrope remains higher than the vapour pressure of the pure substances over a wide temperature range. These data indicate that the mixture remains azeotropic over this entire temperature range.

EXAMPLE 3 This example illustrates the use of the mixtures according to the invention as refrigerants.

The thermodynamic performance data of various mixtures according to the invention were compared with the performance data of the two constituents on their own and with those of CFC 502 (azeotropic mixture containing, by mass, 48.8 % of chlorodifluororaethane and 51.2 % of chloropentafluoroethane) for a standard thermodynamic cycle defined as follows : . condensation temperature: + 30 °C . evaporation temperature : - 40 °C . liquid supercooling : - 15 °C . vapour superheating : + 25 °C Table 3 lists the thermodynamic performance data observed under these conditions for pure HFC 143a, pure FC 218, their mixtures and CFC 502.

TABLE 3 in relation to CFC 502 It can be seen that the mixtures according to the invention offer some advantages over pure HFC 143a, pure FC 218 or CFC 502 , in particular: . a lower compression ratio, improving the volumetric efficiency of the compressor and, as a result, giving rise to lower operating costs for the installation; . a discharge temperature which is lower by at least 10 °C compared with CFC 502 or HFC 143a, which promotes good stability of the mixture in a refrigerating circuit; . a higher available volumetric refrigerating capacity, which in practice, for a given refrigerating capacity, permits the use of a smaller compressor than that defined for the use of CFC 502. 104019/2

Claims (6)

1. Mixture containing, by weight, about 40 to 70 % of 1,1, 1-trifluoroethane and 30 to 60 % of perf luoropropane .

2. Mixture according to Claim 1 , containing, by weight, about 41 % to 60.3 % of 1,1,1- trifluoroethane and 39.7 to 59 % of perf luoropropane

3. Mixture according to Claim characterised in that it contains , by weight, about 55 % of 1,1, 1-trifluoroethane and 45 % of perfluoropropane and corresponds to an azeotropic mixture of low minimum boiling point (about -49.8"C under 1.013 bar).

4. A mixture according to any one of Claims 1 to 3 for use as refrigerant.

5. A mixture according to any one of Claims 1 to 3 for use as aerosol propellant.

6. A mixture according to any one of Claims 1 to 3 for use as plastic foam-expanding agent. For the Applicants DR. R AND PARTNERS